Multi Chassis Switch Cluster technology is used to offer a high degree of protection to network traffic during events that cause a link or switch to go down or come back up. These events could be caused either by failure and recovery of networking components or due to maintenance operations in the network. Switch clustering relies on the following two Intra Cluster components to meet the expectations of a network operator for network resiliency. The first component is a channel for control communication between the switches within a switch cluster. This is used to exchange information relating to forwarding tables, port state information and the like that is applicable to maintaining a resilient switch cluster. The second component is Intra Cluster Traffic paths to carry data traffic between the cluster switches. These are used in the event traffic needs to be redirected to handle common network faults.
Traditionally IST was implemented using dedicated links directly connecting the cluster switches. A cluster switch as it is coming up—keeps the network traffic from outside the cluster away from itself by only allowing directly connected intra cluster links to come up until after it completes the cluster synchronization process. This allows its cluster peers to service the network traffic while the switch is getting ready. This synchronization process is done on the IST control channel. After the cluster synchronization process is complete, other links on the switch are enabled and the switch is then able to forward the traffic.
Virtual IST technology can use any links in the core of the network for the IST. This has the advantage of increasing the robustness of the network by keeping the switch cluster up as long as there is a core network path between the switches within a cluster. Since the Virtual IST technology does not use dedicated IST links—all core network facing links are enabled and core network routing protocols are started in order to bring up the IST control channel.